The UK's chief scientist, Sir David King, says petroleum companies should be looking more closely at the storage of carbon dioxide in ageing oil wells.

He told a climate conference in Exeter, organised by the UK Met Office, that the practice of carbon sequestration could help combat future warming.

Norway's Statoil company has buried CO2 under the North Sea since 1996.

But Sir David believed British firms were concerned about costs and were perhaps looking for tax incentives.

Nevertheless, he argued it was an option UK interests should investigate further.

"In the North Sea, we have got a range of oil wells that are running out," he told reporters in Exeter.

"And we've got all the machinery standing there right now. That machinery could be used for carbon dioxide sequestration experiments."

Making it pay

Statoil's experiment is centred on the Sleipner Field. Waste CO2 that comes up with the extracted methane is separated off and then pumped back under ground. It would normally be vented into the atmosphere.

Climate scientists generally acknowledge that sequestering carbon in this way can play a role in combating global warming.

One obvious limitation is it can only be used to trap and then store emissions from large point sources such as power stations.

I think the oil companies are looking for a tax saving, for a tax break on the oil produced

Sir David King

There are also concerns that the gas could eventually find its way back into the atmosphere, though research on the Statoil project shows that, so far, the carbon dioxide is securely stored.

The technology is available; the key question is cost.

Sir David King's concept could enable companies to generate extra revenue. They would use the pressurised carbon dioxide to pump out the last oil from ageing wells, which would be impossible to extract otherwise.

"In the experiments, pumping carbon dioxide down there, you could squeeze the remaining oil out to pay for the experiment," he said.

This is termed "enhanced oil recovery", and is beginning to come into use, notably in North America.

Trading scheme

UK oil companies remain unconvinced that sequestration is viable in the way that Sir David suggests.

Spokespersons from Shell, BP and the UK Offshore Operators Association, which represents UK companies extracting oil and gas from the North Sea, all told the BBC News website that there was interest in sequestration, but at the moment it was not a favoured option within Britain.

Sir David King believes there is a simple reason for their stance.

"In principle it should pay for itself, but I think the oil companies are looking for a tax saving, for a tax break on the oil produced," he said.

Could CO2 from land power stations realistically be pumped out to sea?

Companies declined to comment on this observation, but there are clearly logistical obstacles.

Many of the UK's large power stations and heavy industry are hundreds of kilometres from the North Sea oil wells, where their emissions would be stored.

The financial climate is also a key factor. Norway has a carbon tax, and Statoil would have to pay for putting carbon dioxide into the atmosphere - storage is cheaper.

British oil companies and power generators are now members of the European Emissions Trading Scheme, which opened for business in January.

This means they will have to keep emissions below a certain target - which the government has yet to define - but they can use various methods to get there, such as improving energy efficiency, investing in renewable energy, planting forests, or buying emissions credits from other companies.

Sequestration is an option - but at this stage, British companies seem set to opt for cheaper ones.